Sunny Luke Talks about the Genetics that Determine Sex

Dr. Luke, chairman of IISAC, discussed his work on human genomics and the genetic basis of gender in his presentation on Sept. 21. (Photo by Ryan Gugerty)
Dr. Luke, chairman of IISAC, discussed his work on human genomics and the genetic basis of gender in his presentation on Sept. 21. (Photo by Ryan Gugerty)

Dr. Sunny Luke, chairman of the International Institute for Scientific and Academic Collaboration (IISAC) and director of the Semester in India program, discussed the genetic and chromosomal differences between the genders in his presentation on Sept. 21 in the Library, titled The Mystery of the Human Gender: X and Y Chromosomes and Beyond…A Neurogenomic Approach.

“Professor Luke, he asked me to tell you, is semi-retired, and still engaged in the Semester in India program,” said College professor Ho Nguyen, introducing Luke to a group of College students and faculty members on Thursday. “Thank you all for coming.”

Luke began the presentation with an introduction to IISAC, an administration centered in New Jersey that organizes research programs for high school and college students internationally to encourage international and cultural education as well as valuable research experience.

Participating in the graduate program in medical genomics at the University of Kerala, Kariavattom in India before coming to the United States and United Kingdom, Luke’s desire to strengthen Indian-American relations and opportunities stems from personal experience. “I’m not offering the controversy here,” said Luke to begin the lecture, referring to the study of male and female formation in the uterus, “but I’m bringing the scientific perspective.”

Luke discussed the idea of sexual dimorphism, or structural and systematic differences between a male and female. The differences stem from the body’s sex chromosomes, or collections of the human genetic code that relate to sexual orientation and development.

While the body has 23 pairs of chromosomes, one pair represents an individual’s sex chromosomes, labeled X or Y. While one of the chromosomes in this pair is always an X, the second chromosome is type Y in males and type X in females (denoting females as XX and males as XY).

“Each of you may have about 30,000 genes in you,” said Luke. “99.99 percent are the same [between individuals], and only the Y chromosome is different.”

The sex chromosomes are a collection of the body’s genes (regions of the genetic code that lead to the production of certain proteins) important for both sexual development and normal functioning. While the X chromosome contains about 1,000 genes, the Y chromosome is much smaller, containing about 10 genes.

However, one of the genes of the Y chromosome, labeled the sex-determining gene or “sex-determining region of Y” (SRY), induces the development of the testes in a fetus, designating that fetus as male. Absence of this gene, possible only when a fetus’ sexual chromosomes are XX, lead to the development of the ovaries, designating that fetus as female.

Identifying the sex of an embryo is impossible during the first two months of development, after which the gonadal ridge of the embryo (as well as the genital tubercle) can be identified. “At the end of the second month, the sex differentiation starts,” said Luke. “By the end of the fourth month, the sex differentiation is complete.” By this point of development, sexual organs are identifiable.

Luke continued the lecture with a discussion of what happens to an individual with a faulty set of sex chromosomes. “If something goes wrong with the genes, effects in the gender will occur,” said Luke.

Examples of this phenomenon included Klinefelter’s syndrome, when a male possesses an extra X chromosome (identified as XXY). An individual with Klinefelter’s syndrome has smaller testes than normal males and is infertile, but can still function as a normal male otherwise. Another disorder, Turner syndrome (or Monosomy X), involves females with a missing X chromosome, causing infertility and a decrease in average height as well as several other physical abnormalities (such as swollen hands and feet or webbed digits).

Luke also mentioned other disorders, including Sawyer syndrome and testicular feminization (or Androgen Insensitivity Syndrome).

The cultural belief differences regarding sex and their roles led into a discussion of what Luke called “the progression of psychological and social sex.” Biological sex (before birth) leads into the development of gender identity after birth, which leads to an understanding of gender roles by the age of three.

At age six, gender roles remain relatively constant, and sexual orientation and attraction develop onwards from the onset of puberty. “The six years after birth are very critical,” said Luke. “Gender role is determined by society, but also comes naturally from gender identity.”

Luke concluded the lecture with a discussion of cues that lead to the activation of sex genes, including visual, olfactory (smell), auditory, and facial cues. Luke also discussed the hijra, a class of individuals in India who, either through cultural and/or biological means, have deemed themselves a “third sex”, neither male or female but individuals with a mix of the two (usually, males with female characteristics and roles).

“Even though I expected more focus on Indian culture and would have loved to hear more information about the Hijras,” said Emma Decker, a junior who attended the lecture, “it was still very interesting to learn about the science behind sex-specific characteristics and about related chromosomal abnormalities.”

Luke also presented the following day, Sept. 22, in a Natural Sciences and Mathematics Colloquium that focuses on his more recent research on stem cells.

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